On-Board Data Handling

The On-Board Data Handling (OBDH) subsystem of a spacecraft is the subsystem which carries and stores data between the various electronics units and the ground segment, via the Telemetry, Tracking and Command (TTC) subsystem.

In the earlier decades of the space industry, the OBDH function was usually considered a part of the TTC, particularly before computers became common on board. In recent years, the OBDH function has expanded, so much that it is generally considered a separate subsystem to the TTC, which is these days concerned solely with the RF link between the ground and the spacecraft.

Functions commonly performed by the OBDH are:

• Reception, error correction and decoding of telecommands (TCs) from the TTC
• Forwarding of telecommands for execution by the target Avionics
• Storage of telecommands until a defined time ('time tagged' TCs)
• Storage of telecommands until a defined position ('position tagged' TCs)
• Measurement of discrete values such as voltages, temperatures, binary statuses etc.
• Collection of measurements made by other units and subsystems via one or more data busses, such as MIL-STD-1553.
• Real-time buffering of the measurements in a data pool
• Provision of a processing capability to achieve the aims of the mission, often using the data collected.
• Collation and encoding of pre-defined telemetry frames
• Storage of telemetry frames in a mass memory
• Downlinking of telemetry to the ground, via the TTC.
• Management and distribution of time signals